Valve caps for standard pneumatic tire valves have traditionally been employed to protect the valve stem from degrading due to corrosion caused by exposure to the environment. The traditional valve caps were typically manufactured from inexpensive polymer-based materials. As such, they were relatively inexpensive and weren't aesthetically appealing. A drawback with the traditional valve cap is that they were easily removed allowing access to the valve actuating member of the valve stem so air could be released from the tire by unauthorized persons.
In recent years, designer caps have come into existence. One such cap is described in U.S. Pat. No. Des. 306,420. The designer caps are aesthetically appealing to the average person and are much more expensive than the traditional valve caps. Typically, a single designer valve cap can cost several dollars. A major drawback with the designer caps is that they are easily removed from the valve stem. Similar to the traditional valve caps, this allows unauthorized person to release air from the tire. More significant, however, it that easy removal raises the possibility that the cap would be stolen, due to its aesthetic appeal. This is a major factor in dissuading purchasers from investing in designer caps. To reduce the probability of unauthorized removal, tamper resistant valve caps have been developed.
U.S. Pat. No. 5,630,687 discloses a prior art tamper resistant valve cap that includes a liner adapted for threaded engagement with a standard pneumatic tire stem valve, a sleeve rotatably mounted with the liner to shroud it and an interlocking feature to selectively prevent axial displacement between the liner and the sleeve. The interlocking feature includes a screw threaded into an aperture in the sleeve, and an annular channel on the liner, positioned to receive the screw. The annular channel has an upper surface, a lower surface and an inner surface disposed between the upper and lower surfaces. The screw is moved so that it extends into the channel resting proximate to the upper surface, but clear of both said lower and inner surfaces. In this fashion, the liner and the sleeve are in a fixed axial position with respect to each other; however, the rotatability of the sleeve with respect to the liner is maintained, preventing removal of the liner from the stem. The rotational movement of the sleeve prevents removing the liner and/or the sleeve from the valve stem. While this valve cap provided superior protection against unauthorized removal of the same, it was subject to damage due to cross-threading of the liner onto the valve stem.
What is needed, therefore, is a theft resistant valve cap which has a reduced probability of cross-threading during operation.